Binder composition for mold and method for producing mold

Abstract: Binder compositions for a mold each comprising a specific alkaline phenol-aldehyde resin are disclosed. Methods for producing a mold using any of the binder compositions are also disclosed.

Description: FIELD OF THE INVENTION The present invention relates to a binder composition for use in the production of a mold, which is aimed at improving the flowability and filling properties of a mixed sand to be obtained by mixing a refractory particulate material with this binder composition. The present invention also relates to a method for producing a mold using this binder composition. BACKGROUND OF THE INVENTION Molds have conventionally been produced by mixing a refractory particulate material with a binder composition, packing the resulting mixed sand into a pattern, and then curing a binder in the binder composition. As the binder, various curable resins such as furan resins, water-soluble phenolic resins, and urethane resins have been used. Of these, water-soluble phenolic resins cure with an organic ester or carbon dioxide gas, thus they are recognized as a binder which can prevent the working atmosphere during the production of self-curing or gas-curing molds from worsening (JP-A-50-130627, JP-B-61-43132, and JP-B-61-37022). (The terms "JP-A" and "JP-B" as used herein mean an "unexamined published Japanese patent application" and an "examined Japanese patent publication", respectively.) The water-soluble phenolic resins herein mean alkaline phenol-formaldehyde resins obtained by subjecting phenol and formaldehyde to polycondensation in the presence of an alkali or by adding an alkali after the polycondensation of these two compounds. However, the production of molds from a mixed sand obtained by mixing a refractory particulate material with a binder composition containing such an alkaline phenol-formaldehyde resin has been defective in that, as compared with the case of using a binder composition containing a furan resin, the mixed sand has so poor flowability that it cannot be densely packed into a pattern. A mixed sand with poor flowability has a drawback that uniform mixing of the refractory particulate material with the binder is difficult. Further, use of a mixed sand with poor pattern-filling properties often causes a rough surface or a reduced surface strength of the resulting mold. Accordingly, there has been a drawback that when a mold obtained using an alkaline phenol-formaldehyde resin as a binder is used in the production of a mold, the resulting cast has defects such as sand inclusion, burning, penetration, and buckle, thus causing a decrease in cast quality. Hence, it has been proposed to incorporate, as a flow accelerator, a fluorine-compound surfactant (JP-A-2-299741) or an aliphatic alcohol (JP-A-3-134067) into a binder composition containing an alkaline phenol-formaldehyde resin. However, fluorine-compound surfactants and aliphatic alcohols have poor compatibility with alkaline phenol-formaldehyde resins and have failed to sufficiently improve the flowability of the mixed sands. In addition, fluorine-compound surfactants and aliphatic alcohols have had another drawback that they are relatively expensive, which makes the resulting casts expensive. On the other hand, it has been proposed to use, as a binder, a phenolic resin obtained by polycondensation of formaldehyde with a bisphenol in place of phenol (JP-A-62-40948 and JP-A-63-40636). In this technique, bisphenol A, bisphenol F, bisphenol C, or the like is used alone as the bisphenol and, hence, the resulting phenolic resin is a binary polymer formed by polycondensation of the bisphenol and formaldehyde. The strength of molds obtained using this bisphenol-formaldehyde binary polycondensation resin improves at a certain degree, but it is not yet been fully satisfactory. That is, there has been a drawback that, although a fully satisfactory mold strength is obtained when the temperature of the refractory particulate material to be mixed with the resin (sand temperature) is high, a low sand temperature results in a considerable decrease in the mold strength. The binder resin has another drawback that a considerable decrease in the mold strength is caused when the amount of a hardener is reduced. It has also been proposed to use, as a binder, a phenolic resin obtained by polycondensation of formaldehyde with a polyhydric phenol used in place of phenol (JP-A-1-166853). However, even with the proposed technique, a sufficient improvement in the strength of molds obtained has not yet been attained. JP-A-56095917 discloses a resol resin produced by co-condensing a phenol, a para-substituted alkyl phenol and an aldehyde in the presence of alkali catalyst followed by dehydrating and concentrating the co-condensate. The dehydration-concentration is performed stably without rapid increase of viscosity. The resulting resol resin is a solid having a high softening point. SUMMARY OF THE INVENTION Under these circumstances, extensive studies were made by the present inventors in order to eliminate the above-described drawbacks of alkaline phenol-formaldehyde resins in the case of mixing with a refractory particulate material. As a result, the present inventors have found that the mixed sand obtained by mixing an alkaline phenol-formaldehyde resin with a refractory particulate material can be improved in flowability and pattern-filling property by modifying the structure of the alkaline phenol-formaldehyde resin itself, that is, by producing a binder resin not by polycondensation of phenol and formaldehyde only, but by copolycondensation of these compounds and a specific phenol compound. The present invention has been accomplished based on this finding. Accordingly, the present invention relates to a binder composition for a mold which comprises an alkaline phenol-aldehyde resin in an aqueous alkaline solution in which the concentration of the phenol-aldehyde resin is from 30 to 75 % by weight, said phenol-aldehyde resin being obtained by copolycondensation of a phenol compound represented by the following formula (1) and/or a polyhydric phenol represented by the following formula (2), a phenol represented by the following formula (3), and an aldehyde compound wherein, R 1 and R 2 each represents hydrogen atom or a hydrocarbon group having 2 or less carbon atoms; wherein R 3 represents hydrogen atom, hydroxy group, or a hydrocarbon group having 2 or less carbon atoms; wherein R 4 represents an aliphatic hydrocarbon group having 3 or more carbon atoms or an aromatic hydrocarbon group, wherein the ratio of the molar amount of said phenol (3) to the total molar amount of said phenol compound (1) and said polyhydric phenol compound is 0.01 to 90 and the ratio of the molar amount of said aldehyde compound to the total molar amount of said phenol compound (1), said polyhydric phenol compound and said phenol (3) is 1.0 to 3.0, and wherein the ratio of the molar amount of all alkali to the total molar amount of the phenol compound (1), the polyhydric compound, and the phenol (3) is from 0.2 to 1.2 and the concentration of the alkaline phenol-aldehyde resin in the alkaline aqueous solution is from 30 to 75 % by weight. The present invention also relates to a method for producing a mold which comprises mixing a refractory particulate material with the binder composition of the present invention to obtain a mixed sand, packing the resulting mixed sand into a pattern, and curing the mixed sand. comprises mixed a refractory particulate material with this binder composition to obtain a mixed sand, packing the mixed sand into a pattern, and curing the mixed sand. DETAILED DESCRIPTION OF THE INVENTION The binder composition for a mold (hereinafter sometimes referred to as the "mold-use binder composition") of the present invention contains an alkaline phenol-aldehyde resin as the main component. The alkaline phenol-aldehyde resin is one obtained by the copolycondensation of a first phenol compound (formula(1)) and/or a polyhydric phenol, a second phenol (formula (3)), and an aldehyde compound. Examples of the phenol compound represented by formula (1) include phenol, cresol, and 3,5-xylenol. Example of the polyhydric phenol represented by formula (2) include resorcinol and catechol. The phenol represented by the above-described formula (3) (hereinafter called "the substituted phenol" in order to distinguish it from the phenol compound (1)) has a substituent such as an alkyl group having 3 or more carbon atoms or a phenol group mainly at the para-position. Examples thereof include nonylphenol, p-tert-butylphenol, isopropenylphenol, and phenylphenol, and they may be used either alone or a mixture of two or more of them. A mixture comprising various phenol compounds such as cashew nut shell liquid is also usable. Examples of the aldehyde compound include formaldehyde, paraformaldehyde, furfural, and glyoxal, and they may be used either alone or a mixture of two or more of them. In the copolycondensation of the phenol compound and/or the polyhydric phenol, the substituted phenol and the aldehyde compound, the molar proportion of each compound is as follows. That is, the ratio of the molar amount of the substituted phenol to the molar amount(s) of the phenol compound and the polyhydric phenol is from 0.001 to 90. If the ratio of the molar amount of the substituted phenol to the molar amount(s) of the phenol compound and the polyhydric phenol in an alkaline phenol-aldehyde resin is less than 0.01 or more than 90, there is a tendency that a mixed sand deteriorates in the flowability and pattern-filling properties even when such an alkaline phenol-aldehyde resin is used. The molar amount(s) of the phenol compound and the polyhydric phenol herein means a molar amount of the phenol compound or the polyhydric phenol when the phenol compound or the polyhydric phenol is used singly, or the total molar amount of the phenol compound and the polyhydric phenol when the phenol compound and the polyhydric compound are used in combination. Further, the ratio of the molar amount of the aldehyde compound to the total molar amount of the phenol compound, the polyhydric phenol and the substituted phenol is from 1.0 to 3.0 ((the molar amount of the phenol compound + the molar amount of the polyhydric phenol + the molar amount of the substituted phenol compound):(the molar amount of the aldehyde compound) = 1:(1.0 - 3.0)). In particular, the ratio of the molar amount of the aldehyde compound to the total molar amount of the phenol compound, the polyhydric phenol and the substituted phenol is more preferably from 1.5 to 2.0. If the ratio of the molar amount of the aldehyde compound to the total molar amount of the phenol compound, the polyhydric phenol and the substituted phenol in the alkaline phenol-aldehyde resin is less than 1.0, there is a tendency that the strength of the resulting mold lowers. On the other hand, if the ratio of the molar amount of the aldehyde compound to the total molar amount of the phenol compound, the polyhydric compound and the substituted phenol is more than 3.0, the resulting alkaline phenol-aldehyde resin emits a strong odor of aldehyde, which may cause a fear that the working atmosphere is impaired. The molar amount(s) of the phenol compound and the polyhydric phenol in this case has the same meaning as defined above. The copolycondensation of the phenol compound and/or the polyhydric phenol, the substituted phenol, and the aldehyde compound is conducted in an aqueous solution to obtain an alkaline phenol-aldehyde resin. The reaction is generally carried out at 50 to 100°C for 1 to 24 hours. In this reaction, it is preferred that the aldehyde compound is gradually added dropwise. A preferred catalyst for use in this reaction is potassium hydroxide (KOH). Since the alkaline phenol-aldehyde resin according to the present invention is formulated into an alkaline aqueous solution, a desired amount of potassium hydroxide may be added during the copolycondensation, or a minimum amount of potassium hydroxide as a reaction catalyst may be added during the copolycondensation and then a desired amount of potassium hydroxide may be supplemented after the completion of the copolycondensation. Further, sodium hydroxide (NaOH) or lithium hydroxide (LiOH) may be added in combination with potassium hydroxide after completion of the copolycondensation so as to adjust the pH value to a desired alkalinity. In the alkaline aqueous solution of the alkaline phenol-aldehyde resin, the ratio of the molar amount of the all alkali(s) to the total molar amount of the phenol compound, the polyhydric phenol and the substituted phenol is from 0.2 to 1.2. It is also essential that the solid content, i.e., the content of the alkaline phenol-aldehyde resin without water, in the alkaline aqueous solution be from 30 to 75 % by weight. The solid content of the alkaline aqueous solution can be determined, for example, by sampling a 2.0 g portion of the solution, drying it by means of a hot air drier at 100°C for 3 hours, and then measuring the weight of the dried matter. The molecular weight of the alkaline phenol-aldehyde resin according to the first embodiment of the present invention is preferably from 500 to 8,000. The molecular weight of the alkaline phenol-aldehyde resin can be measured, for example, by the following manner. First, an appropriate amount of water is added to a resin to be measured, and then H 2 SO 4 is added to the resulting mixture to neutralize the mixture. Thereafter, the precipitate thus formed was separated out by filtration, washed with water, and dried. The dried matter was dissolved in tetrahydrofuran (THF) and then measured for its molecular weight. The measurement can be carried out by GPC method with using polystyrene as the standard. In the copolycondensation to obtain the alkaline phenol-aldehyde resin according to the present invention, an alcohol may exist in the reaction system. By addition of an alcohol in the reaction system for producing the alkaline phenol-aldehyde resin according to the present invention, the flowability and the filling property of the resulting mixed sand can be further improved. Examples of the alcohol include a monohydric alcohol having 2 to 10 carbon atoms such as ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutylalcohol, sec-butyl alcohol, tert-butyl alcohol, n-amyl alcohol, isoamyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, capryl alcohol, nonyl alcohol, and decyl alcohol. These alcohols may be used either solely or a combination of two or more of them. The alcohol is preferably used in such an amount that the ratio of the molar amount of the alcohol to the total molar amount of the phenolic compounds is 0.0001 to 0.5. In this instance, the phenolic compounds mean the phenol compound, the polyhydric phenol and the substituted phenol in the present invention. The mold-use binder composition according to the present invention, which comprises the alkaline phenol-aldehyde resin as the main component, may further contain other ingredients such as the following. For example, it is preferable to incorporate a silane coupling agent for further improving the resulting mold. As the silane coupling agent, any of conventionally known ones of various kinds can be used. Specifically, γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, N-glycidyl-N,N-bis[3-(trimethoxysilyl)propyl]amine, or the like may be used. The flowability and pattern-filling properties of a mixed sand to be obtained by mixing a refractory particulate material with the mold-use binder composition according to the present invention can be further improved by incorporating, into the composition, any of various surfactants including nonionic surfactants, cationic surfactants, anionic surfactants, and ampholytic surfactants or an organic nitrogen compound such as urea, a urea compound, or an amide compound. In the case of using a regenerated sand as the refractory particulate material, the strength of the resulting mold can be improved by incorporating any of various salts of polyvalent metals, such as calcium chloride and aluminum oxide, into the mold-use binder composition. For producing a mold using the mold-use binder composition according to the present invention, either a method of forming a self-curing mold or a method of forming a gas-curing mold may generally be employed. In an example of the method of forming a self-curing mold, 0.1 to 5 parts by weight of an organic ester is added to 100 parts by weight of a refractory particulate material and the mixture is mixed. Thereto is then added 0.4 to 15 parts by weight, preferably 0.6 to 5 parts by weight, of the mold-use binder composition according to the present invention in the form of an alkaline aqueous solution. The resulting mixture is mixed again. The mixed sand thus obtained is packed in a pattern and allowed to stand, whereby the sand cures to give a self-cured mold. In an example of the method of forming a gas-curing mold, 0.4 to 15 parts by weight, preferably 0.6 to 5 parts by weight, of the mold-use binder composition according to the present invention is added, in the form of an alkaline aqueous solution, to 100 parts by weight of a refractory particulate material, and the mixture is mixed. The resulting mixed sand is packed in a pattern for gas curing by means of blowing with compressed air. The sand is then cured by blowing 0.05 to 10 parts by weight of a gaseous or aerosol-form organic ester into the sand, thereby giving a gas-cured mold. As the organic ester, an alkyl formate in which the alkyl group has 1 to 3 carbon atoms, preferably methyl formate can be used. In the case where carbon dioxide gas is employed in place of the gaseous organic ester for curing the mold-use binder composition, a compound having an oxy anion, such as boric acid, a borate, or an aluminate, may be added in an appropriate amount to the binder composition to cure the alkaline phenol-aldehyde resin by the co-action of the compound having an oxy anion and carbon dioxide gas (JP-A-1-224263). As the refractory particulate material for use in producing a mold, any of conventionally known ones of various kinds can be employed. Examples thereof include silica sand mainly composed of quartz, chromite sand, zircon sand, olivine sand, alumina sand, mullite sand, and synthetic mullite sand. It is a matter of course that a sand mainly composed of one obtained by regenerating or recovering any of these sands can be used as the refractory particulate material. The present invention will be explained below in more detail by reference to the following examples, but the invention is not construed as being limited thereto. [Preparation of Mold-use Binder Composition Aqueous Solutions 1-1] To a 50 % aqueous solution of potassium hydroxide were added a phenol compound and/or a polyhydric phenol and substituted phenol in respective amounts determined by the molar ratio shown in Table 1-1. The resulting mixture was stirred to dissolve the compounds. While this solution was maintained at 80°C, an aldehyde compound was gradually added in an amount determined by the molar ratio shown in Table 1-1. The reaction was then continued at 80°C until the weight-average molecular weight of the alkaline phenol-aldehyde resin in the reaction mixture reached 2,500. The time at which the weight-average molecular weight had reached 2,500 was determined from measurements of the viscosity of the reaction mixture. After completion of the reaction, the reaction mixture was cooled to room temperature, and 50 % aqueous potassium hydroxide solution was then added thereto in such an amount that the ratio of the molar amount of the potassium hydroxide to the total molar amount of the phenol compound, the polyhydric phenol and the substituted phenol became 0.85. Thus, an alkaline aqueous solution of an alkaline phenol-aldehyde resin was obtained. To this aqueous solution was added 0.5 part by weight of γ-glycidoxypropyltrimethoxysilane per 100 parts by weight of the solution. In the manner described above, five mold-use binder composition aqueous solutions were prepared. In each binder composition aqueous solution, the solid content of the binder composition was 50 % by weight. In Table 1-1, the item a indicates the ratio of the molar amount of the aldehyde compound to the total molar amount of the phenol compound, the polyhydric phenol and the substituted phenol (i.e., (the molar amount of the aldehyde compound)/(the molar amount of the phenol compound + the molar amount of the polyhydric phenol + the molar amount of the substituted phenol)). The item b indicates the ratio of the molar amount of the substituted phenol to that of the phenol compound and the polyhydric phenol (i.e., (the molar amount of the substituted phenol)/(the molar amount of the phenol compound + the molar amount of the polyhydric phenol)). The a's and b's appearing in the tables that will be given hereinafter are as defined above. [Preparation of Mold-use Binder Composition Aqueous Solutions 1-2] Five mold-use binder composition aqueous solutions 1-2 were prepared by the same method as that for the mold-use binder composition aqueous solutions 1-1 except that the reaction was continued until the weight-average molecular weight of the alkaline phenol-aldehyde resin in the reaction mixture reached 1,800. [Preparation of Mold-use Binder Composition Aqueous Solutions 1-3] A 25 parts by weight portion of each of the aqueous solutions of an alkaline phenol-aldehyde resin which had been obtained after the completion of the reaction in the preparation of the mold-use binder composition aqueous solutions 1-2 was mixed with 5 parts by weight of sodium tetraborate decahydrate and 5 parts by weight of 50 % potassium hydroxide. Thus, five mold-use binder composition aqueous solutions 1-3 were obtained. [Preparation of Mold-use Binder Composition Aqueous Solution 1-4] Phenol was added to a 50 % aqueous solution of potassium hydroxide and dissolved therein with stirring. While this solution was maintained at 80°C, formaldehyde was gradually added in such an amount that the ratio of the molar amount of the formaldehyde to that of the phenol became 1.5. The reaction was then continued at 80°C until the weight-average molecular weight of the phenol-formaldehyde resin in the reaction mixture reached 2,500. The time at which the weight-average molecular weight had reached 2,500 was determined from measurements of the viscosity of the reaction mixture. After completion of the reaction, the reaction mixture was cooled to room temperature, and 50 % aqueous potassium hydroxide solution was then added in such an amount that the ratio of the molar amount of the potassium hydroxide to that of the phenol became 0.85. Thus, an alkaline aqueous solution of a phenol-formaldehyde resin was obtained. To this aqueous solution was added 0.5 part by weight of γ-glycidoxypropyltrimethoxysilane per 100 parts by weight of the solution. In this way, one mold-use binder composition aqueous solution was prepared. In the binder composition aqueous solution, the solid content of the binder composition (the phenol-formaldehyde resin and the silane coupling agent) was 50 % by weight. [Preparation of Mold-use Binder Composition Aqueous Solution 1-5] One mold-use binder composition aqueous solution 1-5 was prepared by the same method as that for the mold-use binder composition aqueous solution 1-4 except that the reaction was continued until the weight-average molecular weight of the phenol-formaldehyde resin in the reaction mixture reached 1,800. [Preparation of Mold-use Binder Composition Aqueous Solution 1-6] A 25 parts by weight portion of the aqueous phenol-formaldehyde resin solution obtained after the completion of the reaction in the preparation of the mold-use binder composition aqueous solution 1-5 was mixed with 5 parts by weight of sodium tetraborate decahydrate and 5 parts by weight of 50 % potassium hydroxide. Thus, one mold-use binder composition aqueous solution 1-6 was obtained. EXAMPLES 1 TO 5 To 100 parts by weight of silica sand as a refractory particulate material was added 0.3 part by weight of triacetin as a hardener. The resulting mixture was mixed. Thereto was then added 1.5 parts by weight of each of the five mold-use binder composition aqueous solutions 1-1 prepared beforehand. The resulting mixtures each was mixed to obtain five mixed sands. The mixed sands were evaluated for their flowability and filling properties by the following method. That is, a test cylinder having an inner diameter of 50 mm and an effective inner length of 100 mm was provided with a support plate at its bottom, and each mixed sand was roughly packed into the test cylinder through a screen having 3 mm mesh. The excess mixed sand above the brim was then scraped off, and the resulting test cylinder was treated with a compactability tester manufactured by George Fischer Ltd. to compact the mixed sand at a squeeze pressure of 10 kg/cm 2 . The resulting decrease in the height of the mixed sand was measured; this height decrease, X mm (= C.B. (compactability)), was regarded as a measure of the flowability and filling properties of the mixed sand. The results obtained are shown in Table 1-1. Lower values of X indicate that the mixed sands have better flowability and filling properties. COMPARATIVE EXAMPLE 1 A mixed sand was obtained in the same manner as in Example 1 except that the mold-use binder composition aqueous solution 1-4 was used in place of the mold-use binder composition aqueous solution 1-1. This mixed sand was evaluated for C.B. The results obtained are also shown in Table 1-1. EXAMPLES 6 TO 10 To 100 parts by weight of silica sand as a refractory particulate material was added 2.0 parts by weight of each of the five mold-use binder composition aqueous solutions 1-2 prepared beforehand. The resulting mixtures each was mixed to obtain five mixed sands. Each mixed sand was evaluated for C.B. in the same manner as in Example 1. The results obtained are shown in Table 1-2. In Table 1-2, the kinds of the phenol compound and/or the polyhydric phenol and others are specified as in Table 1-1. COMPARATIVE EXAMPLE 2 A mixed sand was obtained in the same manner as in Example 6 except that the mold-use binder composition aqueous solution 1-5 was used in place of the mold-use binder composition aqueous solution 1-2. This mixed sand was evaluated for C.B. The results obtained are also shown in Table 1-2. EXAMPLES 11 TO 15 To 100 parts by weight of silica sand as a refractory particulate material was added 3.0 parts by weight of each of the five mold-use binder composition aqueous solutions 1-3 prepared beforehand. Each of the resulting mixtures was mixed to obtain five mixed sands. Each mixed sand was evaluated for C.B. in the same manner as in Example 1. The results obtained are shown in Table 1-3. In Table 1-3, the kinds of phenol compound and/or the polyhydric phenol and others are specified as in Table 1-1. COMPARATIVE EXAMPLE 3 A mixed sand was obtained in the same manner as in Example 11 except that the mold-use binder composition aqueous solution 1-6 was used in place of the mold-use binder composition aqueous solution 1-3. This mixed sand was evaluated for C.B. The results obtained are also shown in Table 1-3. The results in Tables 1-1 to 1-3 clearly show that when an alkaline phenol-aldehyde resin obtained by the copolycondensation of three kinds of the compounds, i.e., a phenol compound and/or a polyhydric phenol, a substituted phenol, and an aldehyde compound, is used as the main component of a binder composition to obtain a mixed sand, the resulting mixed sand has a lower value of C.B. than a mixed sand obtained using a binder composition containing as the main component a phenol-formaldehyde resin produced by the polycondensation of phenol and formaldehyde. Thus, the mixed sands obtained by the methods of Examples 1 to 15 are superior in the flowability and pattern-filling property to the mixed sands obtained by the methods of Comparative Examples 1 to 3. As described above, when the mold-use binder composition of the present invention, which contains a specific alkaline phenol-aldehyde resin as the main component, is used and mixed with a refractory particulate material to obtain a mixed sand, the resulting mixed sand is excellent in flowability and pattern-filling property. Since sufficient mixing is possible when a mixed sand with excellent flowability is used, the binder composition and the refractory particulate material can be uniformly mixed. Further, the mixed sand can be densely packed in a pattern and is hence capable of preventing the resulting mold from having a rough surface or impaired surface strength. Therefore, when casts are produced with a mold obtained using the mold-use binder composition according to the present invention, the occurrence of cast defects such as sand inclusion, burning, penetration, and buckle can be prevented, thus the effect of preventing a decrease in cast quality are attained. Further, use of the mold-use binder composition of the present invention by mixing it with a refractory particulate to obtain a mold can improve the compression strength of the mold as compared with the case of using conventional binder compositions containing a phenol-formaldehyde resin and/or a bisphenol-formaldehyde resin as the main component. Therefore, when casting is conducted with a mold obtained using the mold-use binder composition according to the present invention, the mold surface is less apt to be eroded during melt pouring, thus the effect of giving a cast of excellent quality are attained. Moreover, use of the mold-use binder composition of the present invention enables the production of a mold with a high compression strength even when the refractory particulate material has a low temperature or a hardener is used in a small amount. It is therefore possible to avoid the necessity of warming the refractory particulate material prior to mold production, so that the mold production process can be simplified. In addition, the energy which has been necessary for warming the refractory particulate material can be made unnecessary or reduced. Furthermore, since the hardener amount to be used can be reduced, the cost of hardener can be lowered. Consequently, use of the mold-use binder composition of the present invention produces the effect of enabling the rationalization of mold production. Still further, when the mold-use binder composition of the present invention is used and mixed with a refractory particulate material to obtain a mold, the mold is improved not only in initial compression strength but in compression strength measured after the lapse of a certain time period as compared with the case of using conventional phenolic resins such as phenol-formaldehyde resins. Therefore, when casting is conducted with a mold obtained using the mold-use binder composition according to the present invention, the mold surface is less apt to be eroded during melt pouring, thus the effect of giving a cast of excellent quality are attained. Moreover, the mold-use binder composition of the present invention enables the production of a mold with a high compression strength even when the binder composition is used in a small amount. Since the binder amount in a mold can thus be reduced, the amount of a gas which generates during melt pouring due to the presence of a binder can be reduced, thus the effect of enabling the production of molds having few gas-caused defects are attained. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

Claims: A binder composition for a mold, which comprises an alkaline phenol-aldehyde resin in an aqueous alkaline solution in which the concentration of the phenol-aldehyde resin is from 30 to 75% by weight, said phenol-aldehyde resin being obtained by copolycondensation of a phenol compound represented by the following formula (1) and/or a polyhydric phenol represented by the following formula (2), a phenol represented by the following formula (3), and an aldehyde compound: wherein R 1 and R 2 each represents hydrogen atom or a hydrocarbon group having 2 or less carbon atoms; wherein R 3 represents hydrogen atom, hydroxy group, or a hydrocarbon group having 2 or less carbon atoms; wherein R 4 represents an aliphatic hydrocarbon group having 3 or more carbon atoms or an aromatic hydrocarbon group, wherein the ratio of the molar amount of said phenol (3) to the total molar amount of said phenol compound (1) and said polyhydric phenol compound is 0.01 to 90 and the ratio of the molar amount of said aldehyde compound to the total molar amount of said phenol compound (1), said polyhydric phenol compound and said phenol (3) is 1.0 to 3.0, and wherein the ratio of the molar amount of all alkali to the total molar amount of the phenol compound (1), the polyhydric compound, and the phenol (3) is from 0.2 to 1.2. A method for producing a mold which comprises mixing a refractory particulate material with a binder composition in accordance with claim 1 to obtain a mixed sand, packing the mixed sand into a pattern, and curing the mixed sand. The use of a mold binder composition in accordance with claim 1 in a method of molding in which the binder composition is self-cured or gas-cured.

Inventors: FUNADA HITOSHI, KYOCHIKA NAOKI, MIZUNO WATARU, YOSHIDA AKIRA, FUNADA, HITOSHI, KYOCHIKA, NAOKI, MIZUNO, WATARU, YOSHIDA, AKIRA
Applicants: KAO CORP, KAO CORPORATION
Application year: 1994
Main classification: B22C1
IPC codes: C08G8, B22C1